1. Field of the Invention
The present invention relates to an optical recording medium, a recording/reproduction method and a recording/reproduction apparatus for recording and reproducing information by using radiation of a laser beam or the like.
2. Description of Prior Art
An optical recording medium has attracted attention as a memory having large capacity and high density. A rewritable optical recording medium called as erasable type have been developed. One of the erasable optical recording media has a recording layer made of a thin film which changes the phase between amorphous and crystalline states, and information is recorded and erased by thermal energy due to the laser beam radiation. An alloy film composed of Ge, Sb, Te, In etc. as main components, for example, GeSbTe film, is known as the phase-change material for the recording layer. In many cases, information is recorded by forming marks by partially changing the recording layer to amorphous state while information is erased by crystallization of the amorphous marks. The amorphous state is achieved by radiating a strong laser beam in pulses to heat the recording layer to a temperature not lower than the melting point thereof, and then cooling it at a predetermined or faster rate. The crystallization, on the other hand, is achieved by radiating a comparatively weak laser beam to heat the recording layer to a temperature between the crystallization temperature and the melting point.
Information is recorded in a medium by PWM recording, in which information is represented by mark lengths and space lengths (i.e. edge positions of the front and rear ends of the mark) by forming marks of different lengths with various space sections.
However, in PWM recording, if a strong laser pulse simply equivalent to the mark length is radiated for forming a long mark, the heat generated in the front portion of the mark enhances the temperature increase at the rear portion. Thus, the mark is distorted to have the narrow front portion and the wide rear portion thereof, to deteriorate signal quality. Therefore, as shown in FIG. 4, it is more advantageous to form a mark by using a plurality of laser pulses including the first pulse corresponding to the front end of the mark, intermediate pulses corresponding to the intermediate portion thereof and the last pulse corresponding to the rear end thereof.
Even in this method, however, when an interval between marks is decreased as a result of an increased recording density, the heat generated at the forming of a mark affects the formation of adjacent marks. This leads to a problem that variation of the edge positions of the marks deteriorates the signal quality. The variation of the edge position due to the thermal interference between marks depends on the length of the mark to be recorded and the length of the space sections before and after the mark. In order to solve this problem, Japanese Patent laid open Publication 7-129,959/1995 proposes a signal pattern adaptive recording compensation scheme in which the generation timings xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d of the first and last pulses in FIG. 4 are changed according to the length of the mark and the length of the space sections before and after the mark.
The optimum pulse conditions, however, depend to a larger measure on the characteristics of the medium and the recording/reproduction apparatus. Similarly, optimum servo conditions, such as focal and tracking positions and a gain for determining various servo operations on recording and reproduction, and optimum reproduction signal processing conditions, such as equalizing characteristics and a binarization slice level, are also dependent much on the characteristics of the medium and the recording/reproduction apparatus.
Therefore, each time a recording/reproduction apparatus is activated for recording with an optical recording medium mounted therein, test recording is carried out while changing recording/reproduction conditions such as the pulse conditions, the servo conditions and/or the reproduction signal processing conditions. Then, the quality of the reproduced signals with the measurement is compared to determine the optimum recording/reproduction conditions, and the recording of information is performed based on the optimum recording/reproduction conditions. Then, it is a problem that the action called as learning for determining the optimum recording/reproduction conditions is always required on activation to make a waiting time longer.
An object of the present invention is to provide an optical recording medium, a recording/reproduction method and a recording/reproduction apparatus therefor that can shorten a time required for the learning and realize a short activation time.
In one aspect of the invention, an optical recording medium for recording the information by forming a mark with laser pulses radiated thereon, comprises a information recording area provided for recording the information, and a recording/reproduction conditions recording area, to which recording by a recording/reproduction apparatus is possible, provided for recording recording/reproduction conditions representing setting values for the recording/reproduction apparatus for recording or reproducing information. Preferably, the recording/reproduction conditions recording area has a capacity enough to record a plurality of sets of the recording/reproduction conditions. Preferably, the recording/reproduction conditions recording area is further used for recording apparatus information for identifying the recording/reproduction apparatus which uses the recording/reproduction conditions. Preferably, the optical recording medium further comprises a test recording area provided for test recording of a specified signal to measure a quality of reproduced signal. The recording/reproduction conditions recording area and the test recording area is preferably interposed between the lead-in area and a region for recording the information.
In a second aspect of the invention of recording/reproduction method for recording/reproducing information by using marks formed with radiation of laser pulses on an optical recording medium, wherein lengths of the marks and those of space sections before and after the marks represent the information, recording/reproduction conditions are read from a recording/reproduction conditions recording area in the medium, to which recording by a recording/reproduction apparatus is possible. Then, information is recorded or reproduced based on the recording/reproduction conditions, wherein a plurality of pulses are radiated from a front end to a rear end of a mark when the mark is formed.
In a third aspect of the invention of a recording/reproduction method for recording/reproducing information, recording/reproduction apparatus information for identifying a recording/reproduction apparatus which uses the recording/reproduction conditions are read from a recording/reproduction conditions recording area in the optical recording medium, besides the recording/reproduction conditions. Then, information is recorded or reproduced based on the recording/reproduction conditions accompanying the recording/reproduction apparatus information coinciding with the recording/reproduction apparatus to be used, wherein a plurality of pulses are radiated from a front end to a rear end of a mark when the mark is formed.
Preferably, in the above-mentioned two recording/reproduction methods, test recording is performed to determine optimum recording/reproduction conditions for a recording/reproduction apparatus by changing recording/reproduction conditions, and the obtained result is recorded in the recording region in the optical recording medium. Thereafter, recording or reproduction is performed based on the recording/reproduction conditions read from the recording region.
In a fourth aspect of the invention, an optical recording/reproduction apparatus records and reproduces information with marks formed with radiation of laser pulses on an optical recording medium, wherein lengths of the marks and those of space sections before and after the marks represent the information. In the apparatus, a spindle motor rotates the optical recording medium. An optical head radiates a laser pulse with a laser diode onto the optical recording medium, a servo circuit drives the optical head, and a laser driver drives the laser diode according to pulse signals for recording information. A pulse controller generates pulses for driving the laser driver, wherein a plurality of pulses are generated to radiate from a front end to a rear end of the mark to record the information. An equalizer corrects frequency characteristic of reproduction signal, and a binarizing circuit converts the corrected reproduction signal to a binarized signal. Further, the apparatus comprises a storage device for storing recording/reproduction conditions read from a recording area provided for storing recording/reproduction conditions in the optical recording medium, and at least one of first setting means for setting pulse conditions for the pulse controller in accordance with the recording/reproduction conditions, second setting means for setting servo conditions for the servo circuit, third setting means for setting equalizing conditions of reproduction signal to the equalizer and fourth setting means for setting a binarization slice level to the binarizing circuit.
An advantage of the present invention is that shorten a time required for the learning and realize a short activation time.